Arithmetic logic unit (ALU)
Name:
Date:
Class:
A
Quick Questions
Shade in the A or B circle for each question.
1. What does the ALU do in the CPU?
2. Which task is carried out by the ALU?
3. Where is the result of an ALU calculation usually held?
4. Which of these is a logical operation the ALU can perform?
5. The ALU compares 7 and 5 to decide if 7 > 5. What type of operation is this?
B
Match the Pairs
Draw a line connecting each item on the left to its match on the right.
| Left column | Right column | |
|---|---|---|
| 1ALU | AThe CU does not do calculations or comparisons. The ALU does arithmetic and logic. The CU only controls and coordinates. | |
| 2ACC <- ACC + 5 | B(age >= 16) AND (hasTicket == TRUE) | |
| 3The ALU performs arithmetic, such as subtracting one number from another | CThe part of the CPU that carries out arithmetic calculations and logical comparisons | |
| 4The ALU performs logical decisions, such as comparing two values with AND | Dresult = 20 - 8 | |
| 5The control unit (CU) adds the numbers 4 + 3 and does the comparisons. | EThe ALU does arithmetic (add, subtract) and also logical operations (AND, OR, NOT, comparisons). | |
| 6The ALU can only add numbers. It cannot do logic such as AND, OR, NOT. | FThe ALU adds 5 to the value held in the accumulator and stores the result back in the accumulator |
C
Definitions
ALU
D
Fill in the Blanks
Complete each line of code by filling in the missing parts.
1.
ACC ← 10
ACC ← ACC _ 5
2.
ACC ← 20
ACC ← ACC _ 8
3.
IF age >= 16 ___ mark > 50 THEN
4.
IF a = 1 __ b = 1 THEN
5.
___ ← ACC + 5
E
Spot the Error
Shade in the letter of the line that contains an error.
Question 1
A
ACC ← 8
B
B ← 3
C
ACC ← ACC - B
D
OUTPUT ACC // 11
Question 2
A
ACC ← 10
B
ACC ← ACC + 4
C
OUTPUT ACC // 6
Question 3
A
A ← 7
B
R ← A > 5 AND A > 10
C
OUTPUT R // TRUE
Question 4
A
LOCKED ← TRUE
B
// ALU applies NOT
C
OPEN ← LOCKED
D
OUTPUT OPEN // FALSE
Question 5
A
ACC ← 65
B
PASS ← 50
C
R ← ACC <= PASS
D
OUTPUT R // TRUE
Answer Key
Arithmetic logic unit (ALU)
Section A: Quick Questions
Q1
B — Carries out arithmetic calculations and logical comparisons
Q2
A — Adding two numbers together
Q3
B — In the accumulator (ACC)
Q4
A — AND
Q5
A — A logical comparison
Section B: Match the Pairs
Q1
ALU → The part of the CPU that carries out arithmetic calculations and logical comparisons
Q2
ACC <- ACC + 5 → The ALU adds 5 to the value held in the accumulator and stores the result back in the accumulator
Q3
The ALU performs arithmetic, such as subtracting one number from another → result = 20 - 8
Q4
The ALU performs logical decisions, such as comparing two values with AND → (age >= 16) AND (hasTicket == TRUE)
Q5
The control unit (CU) adds the numbers 4 + 3 and does the comparisons. → The CU does not do calculations or comparisons. The ALU does arithmetic and logic. The CU only controls and coordinates.
Q6
The ALU can only add numbers. It cannot do logic such as AND, OR, NOT. → The ALU does arithmetic (add, subtract) and also logical operations (AND, OR, NOT, comparisons).
Section C: Definitions
Q1
ALU — Arithmetic logic unit: the part of the CPU that does calculations (add, subtract) and logic decisions (AND, OR, NOT, comparisons). Results are held in the accumulator.Section D: Fill in the Blanks
Q1
ACC ← 10
ACC ← ACC + 5Q2
ACC ← 20
ACC ← ACC - 8Q3
IF age >= 16 AND mark > 50 THENQ4
IF a = 1 OR b = 1 THENQ5
ACC ← ACC + 5Section E: Spot the Error
Q1
C — The ALU should ADD 8 and 3 to give 11. Subtracting would give 5. Line 3 should be ACC ← ACC + B.
Q2
B — The ALU must subtract 4 from 10 to get 6. Adding gives 14. It should be ACC ← ACC - 4.
Q3
B — 7 is not greater than 10, so the AND comparison would be FALSE. The ALU should test A < 10 so the result is TRUE.
Q4
C — The comment says the ALU applies NOT, which reverses TRUE to FALSE. Without NOT, OPEN would be TRUE. It should be OPEN ← NOT LOCKED.
Q5
C — 65 is greater than or equal to 50, so the comparison gives TRUE. Using <= would give FALSE. It should be R ← ACC >= PASS.